This invention relates to material mixing or blender devices for use in various industries, and more particularly to such apparatus as intended for use in solid-solids or liquid-solids blending operations.
In the prior art, various type mixers or blenders have been developed for use in blending solid-solids or liquids-solids to achieve dry or wet blends of materials. These prior art mixers and blenders have comprised variously shaped tumbler devices with or without internal baffles, agitators, intensifiers or the like and as liquid dispersion or attrition bars.
One such prior art blender is known as a cone or double cone blender. This blender derives its name from its shape and comprises a vertical cylinder with conical ends which rotate about a horizontal axis. The double cone blender suffers from the disadvantage of symmetrical flow pattern with maximum flow at the center. This tends to fill the space mostly from the middle, leaving the material near the trunnion relatively unmixed. Consequently, excessively long mixing periods are required for blending because of poor axial flow of materials.
Another form of solid-solids blender known in the art is a ribbon blender. Such blender comprises a stationary trough-type shell fitted with longitudinal shaft on which are mounted arms supporting slender spiral ribbons. It is one of the oldest mechanical mixing devices used for solid-solids mixing. This blender is effectively used for low-density solids, materials that aerate readily and light pastes. It is not recommended for precision blending, abrasive materials, material that packs, or when frequent cleaning is required. It is also not suitable for dense materials because of excessive power requirements. Unmixed material tends to accumulate at ends and at shell wall because of blade clearance. Ribbon blenders also suffer from the disadvantage of poor axial flow of materials.
Still another form of blender is my twin shell blender developed in the late 1940's and patented July 4, 1950, under U.S. Pat. No. 2,514,126. This blender comprises two opposed simple cylinders formed into a "V". An outgrowth of the simple cylinder, the Twin-Shell overcomes discharge problems and creates additional mixing action at the center. This extra action is responsible for faster, more efficient blending action than produced by a single cylinder and relies for its primary mixing action due to intermeshing of solids at the center line.
These and various other forms of blenders are illustrated and described in Patterson-Kelley Company, Division of Taylor Wharton Co.-Harsco Corporation Bulletin PED-2, "Patterns of Precision in Processing Equipment", Copyright 1975.
The devices of the prior art have been efficient only to limited degrees for the purposes intended, especially when operating upon differently sized materials or materials of substantially different specific gravities. The ideal blender for handling solid particles would have a number of desirable qualities in perfect balance. Most important are efficient mixing action, gentle mixing action, optional intensive mixing, dust-tight operation, complete discharge, cleanability, low maintenance and installed costs.
I have unexpectedly found that these desirable qualities can be obtained in a modified twin shell blender which has been modified such that the blender is formed of two shells having unequal axial dimensions. This construction forces a cross flow pattern of materials during rotation of the shell about a horizontal axis which provides an unexpected synergistic mixing action and which dramatically reduces the mixing time over that normally experienced in conventional twin shell blenders.
It is believed that this synergistic mixing action is attributable to a substantial decrease in the static charge build-up that is normally developed from cross flow of particles and the ability to achieve full blend conditions with a minimum of work input. It is known, for example, that when mixing certain materials such as polymers and/or cosmetic powders, the surface properties of the particles effect spreading or cross flow and that these surface properties are affected by the work input or blend time. Too much work input can cause an uneven charge build-up on the particles. The net result is that a polarity condition develops which retards cross-flow. Cross flow of materials enhances the break down of this static charge condition and also minimizes its buildup. Thus, the forced effect of cross flow which minimizes mixing time also results in a lesser charge build-up which in turn further enhances cross-flow.
It is an object of the present invention to provide an improved rotating or "tumbler" type blending mill, comprising a casing structure of novel shape which when rotated produces an axial flow which is essential for attaining a precise blend.
Another object of the invention is to provide an improved blending mill for the purposes aforesaid which is of structurally simple and rugged form, and which may be fabricated in accord with a novel and economical manufacturing procedure.
Another object of the invention is to provide an improved blending mill for the purposes aforesaid which operates to provide improved efficiency and economy in material blending operations.
A further object of the invention is to provide an improved tumbler type blending mill having a gentle mixing action and which enables precise blending of materials.
Other objects and advantages of the invention will be readily apparent from the specification which provides a detailed description of the invention, particularly when taken in connection with parts throughout the several views.